Steel Connections Design Issues
Dr. Seshu Adluri
ntro uct on
Steel Connections Unlike concrete, connections in steel structures need s ecial desi n
Bolts, Rivets and Welds are typical
Steel Connections -Dr. Seshu Adluri
o n ng
ruc ura e emen s
Mechanical fastenings
Welding
es ve on ng
Steel Connections -Dr. Seshu Adluri
Rivets o ng Stud Welding Threaded Fasteners & Nails Ex ansion Bolts Adhesive-held fasteners Mechanically formed joints
Steel Connections -Dr. Seshu Adluri
ve s
Old style connectors Permanent, Need field heating and head forming Tension on cooling is not estimated accurately Load distribution is not as good as that for bolts
Steel Connections -Dr. Seshu Adluri
ve s
Old style connectors Permanent, Need field heating and head forming Tension on cooling is not estimated accurately Load distribution is not as good as that for bolts
Steel Connections -Dr. Seshu Adluri
Pins
Rarely used compared to bolts and welds
Special projects only
Golden gate bridge approaches
Steel Connections -Dr. Seshu Adluri
o s
Steel Connections -Dr. Seshu Adluri
o ts
Steel Connections -Dr. Seshu Adluri
o ts
Carbon Steel Bolts
Normal stren th A307
Similar to ordinary machine bolts Lower Strength, low load/shear connectors
-
, , , –Sec. 3, CISC Handbook Heat treated for greater strength
.
Can also be used in Friction Connections Can be used with or without washers Snug tight bolts (allow slippage) Pre-tensioned bolts (slip critical) o ave e same u ma e s reng
Steel Connections -Dr. Seshu Adluri
a er a
e av our
Steel Connections -Dr. Seshu Adluri
a er a
e av our
Steel Connections -Dr. Seshu Adluri
o s
Snug tight bolts (allow slippage) Easy to install (till about the first impact using the . 10-20% of tension strength
Pre-tensioned bolts (slip critical –no slip) ost y to nsta , nee nspect on Repeated loadings, bridges, communication towers, load reversals, impact, cranes, direct tension, etc. Safety against twist-off, all bolts yield
Both have the same ultimate strength
Steel Connections -Dr. Seshu Adluri
re- ens one
o s
Installation
Turn of the nut method (Table 8 –CSA-S16)
1/3 turn for Lb < 4db
1/2 turn for 4db < Lb < 8db (or 200 mm)
Tension indicator washers (ASTM F959) Cl. 23.8.3
Torque wrench
Strain gauges, etc.
Bolt tension as per Table 7, CSA-S16
Steel Connections -Dr. Seshu Adluri
re ens on e ec
Steel Connections -Dr. Seshu Adluri
re ens on e ec
Steel Connections -Dr. Seshu Adluri
ens on con ro e
Wrench grips both the nut & bolt
When required torch reached,
o s
End twists off A plunger inside discharges the splined end
Steel Connections -Dr. Seshu Adluri
o
mens ons
Standard dimensions thread lengths, bolt lengths for different grips
Handbook p.6-152 to 6-156
Gauge dist. P.6-162
Nominal Bolt Size
Length Added
5/8”
7/8”
¾”
1”
7/8”
1 1/8”
1”
1 ¼”
Steel Connections -Dr. Seshu Adluri
o s
Tension indicator washers
Steel Connections -Dr. Seshu Adluri
ens on n ca or
as ers
ASTM F959 washers (Cl. 23.8.3)
Steel Connections -Dr. Seshu Adluri
Washers
Protrusions (Gap) Protrusions flatten as Bolt is tightened Visually ins ected to ensure that protrusions are flat (gap closed
Steel Connections -Dr. Seshu Adluri
Washers
Load Indicator Washers with a Visible Dye that squirts out when the was er as su c en y flattened
Steel Connections -Dr. Seshu Adluri
on the joint
Steel Connections -Dr. Seshu Adluri
oa vs.
onga on
Steel Connections -Dr. Seshu Adluri
re- ens on e ec
Steel Connections -Dr. Seshu Adluri
Pre-tension effect on tension force on
As the applied tension on the joint increases, the bolt elongates a little and eventually elongates enou h to the len th before tightening. At that point, the bolt pretension effect disappears and the joint will behave as if the retension had never been there. If the joint is unloaded at that point, the clamping effect due to pretension will return.
Steel Connections -Dr. Seshu Adluri
o s
“Guide to Design Criteria for Bolted and Riveted Joints” by Geoffrey L. Kulak, John W. Fisher & John H. A. Struik at: .
.
.
RCSC: Research Council on Structural Connections
http://www.boltcouncil.org/index.html
Steel Connections -Dr. Seshu Adluri
ot
ea s
Required
Steel Connections -Dr. Seshu Adluri
Bolted ons
Steel Connections -Dr. Seshu Adluri
Steel Connections -Dr. Seshu Adluri
Steel Connections -Dr. Seshu Adluri
Joints
Steel Connections -Dr. Seshu Adluri
Typical Bolted Joints
Steel Connections -Dr. Seshu Adluri
ear ng ype o s n
ear
Steel Connections -Dr. Seshu Adluri
Steel Connections -Dr. Seshu Adluri
o s n
ear
Steel Connections -Dr. Seshu Adluri
o
ear ng e ec
Steel Connections -Dr. Seshu Adluri
o s n ens on a ure
Steel Connections -Dr. Seshu Adluri
o
oc
ear ou e ec
Steel Connections -Dr. Seshu Adluri
ear ag e ec
Steel Connections -Dr. Seshu Adluri
es gn or o s
Shear:
V = 0.6
nmA F
.
. =0.8
>V
-
(Cl. 13.12.1.2)
Bearing: .
.
Br = 3
br tdb
n Fu-plate
>Vf ,
br =0.8
>Tf ,
b
. .
Tension:
Tr = 0.75
b
AbFu-bolt
=0.8
(Cl. 13.12.1.3)
Slip resistance
(Cl. 13.12.2.2) :
Vs = 0.53 c1 Ks mn AbFu-bolt >V
Combined:
V f V r
2
T f + T r
2
≤1
V V s
(table 3 –CSA-S16)
+ 1.9
T nAb Fu
≤1
Steel Connections -Dr. Seshu Adluri
,
,
.
If threads are interce ted in shear reduce A to 70
spacing:
Min. Edge dist.: Table 6 (based on db & edge type)
Max. Edge dist.: 12t or 150mm
End distance:
Bolt hole diam.: db + 2mm (or 1/16”)
Eff. hole diam.: hole diam.+2mm (for punched holes) h
b
2.7db (usually 3db) Cl. 22.3.1
Table 6 or 1.5 db
h
b
Installation and inspection: Cl. 23, Washers: Cl. 23.5
Steel Connections -Dr. Seshu Adluri
It’s cheesy cartoon time!
Bolt Power!
She has the hex bolt
Together, bolt and nut can keep the structure intact! Steel Connections -Dr. Seshu Adluri
ccen r c o e connec on L = Moment/Load
8
1
7
2
b b
eccentric load 5
4
D
Steel Connections -Dr. Seshu Adluri
ccen r c o e connec on
Rotation effect only
Direct shear effect only
Steel Connections -Dr. Seshu Adluri
ccen r c o e connec on
Resultant of both rotation and direct shear effects Steel Connections -Dr. Seshu Adluri
o s–
ry ng ac on
Steel Connections -Dr. Seshu Adluri
o s–
ry ng ac on
Steel Connections -Dr. Seshu Adluri
Steel Connections -Dr. Seshu Adluri
o s–
ry ng ac on
Use procedure in the Handbook (no code clauses
Steel Connections -Dr. Seshu Adluri
Prying action
Steel Connections -Dr. Seshu Adluri
MIG (Metal Inert Gas) welding
Flux core welding
Steel Connections -Dr. Seshu Adluri
(Tungsten Inert Gas) welding
Stick welding torch (tig)
Steel Connections -Dr. Seshu Adluri
Automated Weldin
Plasma Welding & Cutting Tungsten Inert Gas Arc Welding (TIG)
laser welding wire feed system Steel Connections -Dr. Seshu Adluri
e s
electron microscope
Steel Connections -Dr. Seshu Adluri
T es of welds
Steel Connections -Dr. Seshu Adluri
Fillet welds
Steel Connections -Dr. Seshu Adluri
Fillet welds
Steel Connections -Dr. Seshu Adluri
u
e s
Steel Connections -Dr. Seshu Adluri
e
ng sym o s
Steel Connections -Dr. Seshu Adluri
e
ng sym o s
Steel Connections -Dr. Seshu Adluri
e
ng sym o s
Steel Connections -Dr. Seshu Adluri
e
ng sym o s
Steel Connections -Dr. Seshu Adluri
es gn o
e s = . Vr = 0.67 Vr = 0.67
.
.
w
Base metal: Weld metal:
Fillet Welds
w
=0.67 = Vr = 0.67
Am Fu w A w Xu w
Weld metal:
w
Aw Xu (1+0.5sin1.5 )Mw governs if
> 45o for 350W
Flare bevel weld in OWSJ:
Vr = 0.67
w
Aw Fu
Aw = 0.5 wf L
Steel Connections -Dr. Seshu Adluri
e
s zes, e c
Min. groove depths for different situations applicable
Max. size:
sect ons Min. size:
Dmax = t-2 mm Dmax = t Dmax = 0.75t
t > 6mm t ≤ 6mm for the rounded edges of rolled
Dmin = 5 mm tmax ≤ 12mm Dmin = 6 mm 12mm ≤ tmax ≤ 20mm D = 8 mm 20mm ≤ t Min length Lmin = max (4D, 40 mm) Lap Joints: min. lap length Llap = 5tmin or 25 mm
Steel Connections -Dr. Seshu Adluri
ro ems n
e
p acement
Steel Connections -Dr. Seshu Adluri
ro ems n
e
p acement
Alignment not very good
Steel Connections -Dr. Seshu Adluri
in Weld p acement
Steel Connections -Dr. Seshu Adluri